This invention relates in general to signal generation, and in particular, to a method and apparatus for producing ramp signals having rounded starts and stops.
When controlling the speed of motors, particularly motors used with elevators, mine hoists, metal rolling mills, paper mills, etc., it is desirable to have smooth and rapid starts as well as smooth and rapid stops. In elevators and mine hoists it is desirable to have smooth starts and stops in order to provide a comfortable and pleasing ride for the passengers; it is also desirable to have relatively rapid starts and stops to speed the transportation of the passengers and eliminate any unnecessary delays. There must, of course, be some compromise between speed and smoothness of ride; the ride could be very smooth by providing slow starts and stops, but this would not be very rapid; on the other hand, the speed could be increased by having sudden, jerky, starts and stops.
With metal rolling mills, the stops and starts must be controlled in order to prevent excessive stressing of the metal. If the starts and stops are too sudden, the metal undergoing treatment is exposed to high stresses and strains, producing an undesirable product. If, on the other hand, the stops and starts are too slow, valuable time, and accordingly production, is lost.
A similar problem occurs in paper mills. The paper when being wound, must be kept under a carefully controlled tension. If the tension becomes too great, due to either a sudden stop or start, the paper may tear or break; if the tension becomes too low, the paper may crease and fold while being wound.
One prior art method of motor control, for use in an elevator application, is described in the Hitachi Review, Vol. 21, No. 6, dated June 1972, on pages 243-251. That description discloses the use of a speed pattern circuit as shown in FIG. 5 of said review. The aim is to obtain trapezoid wave acceleration characteristics (see FIG. 12 of said review) which are smooth at each inflection point in the trapezoid acceleration characteristics.
Various other methods for regulating the speed and acceleration of elevators or motors can be found in the following U.S. patents: U.S. Pat. No. 3,526,300 dated Sept. 1, 1970; U.S. Pat. No. 3,350,612 dated Oct. 31, 1967; U.S. Pat. No. 3,552,524 dated Jan. 5, 1971; and U.S. Pat. No. 3,377,855 dated Dec. 11, 1973.